Mathematics Class 7
Number Play
Test number tricks, add odd and even, build magic squares, count rhythms, solve letter puzzles.
16 lessons · ~103 min total
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Lessons in this topic
- 0 Start here A roadmap: digit sums, odd and even, magic squares, rhythms, puzzles, proofs. · 4 min You are here
- 1 What a digit sum remembers Adding a number's digits gives a smaller number that leaves the same amount over on 9 and on 3. · 6 min
- 2 Why adding the digits knows anything Every column is a run of nines plus one, and a run of nines never gets in the way of 3 or 9. · 7 min
- 3 Odd and even, multiplied A product is odd only when both numbers are odd — a different rule from the one adding follows. · 6 min
- 4 Turn it round and subtract Take the smaller of a two-digit number and its reverse from the bigger: the answer is 9 times the gap between the two digits. · 7 min
- 5 Several clues at once Clues can be applied in any order, some rule nothing out, and what survives may be one number, several, or none. · 7 min
- 6 The case that breaks it A claim can fit nine cases and die on the tenth — and one failed case is enough to kill it for good. · 7 min
- 7 Saying why, in order A reason is a list of sentences, each using only earlier ones. One worked example is not one of them. · 7 min
- 8 Odd and even, added The count of odd numbers decides if a sum is odd. · 6 min
- 9 Magic squares A 3 by 3 magic square's sum is 3 times its centre. · 7 min
- 10 Counting rhythms Each rhythm count is the two before it, added. · 7 min
- 11 Letters for digits Solve a letter puzzle: units column first, then the next. · 7 min
- 12 Even or odd expressions With an even number in front of n, the plain number decides. · 7 min
- 13 Checkpoint: sums, squares and sequences Check odd and even sums, magic squares, rhythms and parity. · 5 min
- 14 The big picture Twelve ideas on one screen. · 5 min
- 15 Track quiz Cheat-sheet table plus a reveal quiz — one question per idea. · 8 min
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